With the advent of more powerful central processor units (CPU's) and higher bandwidth bus structures, disk drive performance has become a significant limiting factor in overall computer system performance. Specifically, disk drives tend to impose data access delays on the order of several milliseconds, as opposed to the nanoseconds required to access data from electronic storage, hence there is a need to reduce actuator access times in order to enable more rapid retrieval of data from the tracks of a recording surface in a disk drive.
Contemporary disk drives typically include a rotating rigid storage disk and a head positioner for positioning a data transducer at different radial locations relative to the axis of rotation of the disk, thereby defining numerous concentric data storage tracks on each recording surface of the disk. The head positioner is typically referred to as an actuator. Although numerous actuator structures are known in the art, in-line rotary voice coil actuators are now most frequently employed due to their simplicity, high performance, and their ability to be mass balanced about their axis of rotation, the latter being important for making the actuator less sensitive to perturbations. A closed-loop servo system is employed to operate the actuator and thereby position the heads with respect to the disk surface. The dynamic characteristics of hard disk drive actuator servo systems are such that higher servo system performance may be achieved when the natural mechanical vibration modes of the head and suspension structures do not occur at or near the servo sampling frequency or its aliased variants.
The read/write transducer, which may be of a single or dual element design, is typically mounted upon a ceramic slider structure having an air bearing surface for supporting the transducer at a small distance away from the surface of the moving medium. Single element designs typically require two wire connections while dual element designs require four. Magnetoresistive (MR) heads, in particular, generally require four wires. The combination of an air bearing slider and a read/write transducer is also known as a read/write head or a recording head.
Sliders are generally mounted to a gimbaled flexure structure attached to the distal end of a suspension's load beam structure. A spring biases the load beam, and therethrough the head, towards the disk, while the air pressure beneath the head pushes the head away from the disk. The equilibrium distance then determines the "flying height" of the head. By utilizing such an "air bearing" to support the head away from the disk surface, the head operates in a hydrodynamically lubricated regime at the head/disk interface rather than in a boundary lubricated regime. The air bearing maintains spacing between the transducer and the medium which reduces transducer efficiency, however, the avoidance of direct contact vastly improves the reliability and useful life of the head and disk components. Demand for increased areal densities may nonetheless require that heads be operated in pseudo contact or even boundary lubricated contact regimes, however.
The disk drive industry has been progressively decreasing the size and mass of the slider structures in order to reduce the moving mass of the actuator assembly and to permit closer operation of the transducer to the disk surface, the former giving rise to improved seek performance and the latter giving rise to improved transducer efficiency that can then be traded for additional track density. The size (and therefore mass) of a slider is usually characterized with reference to a so-called standard 100% slider (minislider). The terms 70%, 50%, and 30% slider (microslider, nanoslider, and picoslider, respectively) therefore refer to more recent low mass sliders that have linear dimensions that are scaled by the applicable percentage relative to the linear dimensions of a standard minislider.
Although smaller, low mass heads can provide both performance and economic advantages, the reductions in physical slider dimensions give rise to numerous problems that do not necessarily scale linearly with the dimensional changes. If, for example, the size and load force on the slider are simply halved, the air bearing stiffness in the pitch direction will be reduced on the order of 1/8. A flexure must have sufficient compliance to allow the slider adequate freedom to pitch and roll in order to maintain the trailing edge of the slider at the desired distance from the moving media surface because the failure to maintain adequate spacing can lead to signal modulation, data loss, or even catastrophic failure of the head or disk components. Accordingly, flexures designed for use with picosliders must have highly compliant gimbals, which are typically implemented by the flexure structure.
Even assuming a highly compliant gimbal structure, however, a significant additional problem arises in that the wiring that interconnects the disk drive electronics to the transducer(s) on the slider contributes a nontrivial degree of parasitic stiffness to the gimbal structure, particularly when using dual element heads, which generally require 4 discrete wires.
Finally, the requisite wire structure adds mass to the overall head/gimbal assembly (HGA). The current wire gauges employed with picosliders are about as small as can be practically and reliably manufactured and assembled. The mass of common prior art wires, including an insulating tube, can even exceed the entire mass of certain thin film fabricated HGA's designed for use in contact or pseudo-contact recording applications. Thus in current advanced HGA designs, a semi-tubeless wire design is employed wherein the dielectric tube does not extend along the length of the load beam. Although this reduces the mass of the HGA, it does create additional reliability problems because of the inherent fragility of long unprotected runs of small wires and because of the increased potential for shorting the wires to the each other or to the load beam. Accordingly, there exists a need for a more robust wiring structure for an HGA that does not deleteriously affect either gimbal compliance or HGA mass.
Prior art attempts to address these problems include fully integrated head/flexure/suspension structures that are fabricated via conventional photolithographic materials deposition and patterning techniques, laminated stainless steel suspensions structures which utilize the beam and gimbal structures as conductors, and stainless steel suspensions having deposited insulators and conductors. Although photolithographically deposited suspensions can be particularly low in mass, the mechanical properties of the deposited beams have not proven suitable for high performance servo operation, while the deposited gimbal structures have been relatively fragile. Laminated stainless steel suspensions appear to have better mechanical performance than deposited suspensions, however, the laminated stainless steel designs have higher parasitic capacitances than prior art designs and are relatively difficult to manufacture with repeatable precision. Additionally, because the stainless steel used in the gimbal structure is relatively stiff, the mechanical alterations required to achieve high compliance result in a gimbal structure that is also relatively fragile and difficult to manufacture. Deposited conductor stainless steel suspensions are easier to fabricate but have similar problems with respect to the robustness and manufacturability of the gimbal structure.
Referring to the drawings, wherein like characters designate like or corresponding parts throughout the views, FIG. 1 shows an head/gimbal assembly (HGA) 2 in accordance with the prior art. The HGA includes load beam 14 which is attached to a baseplate 4 which is in turn mounted to an actuator arm (not shown).
An inline rotary voice coil actuator structure (not shown) typically includes a plurality of actuator arms that are vertically registered to accommodate a plurality of HGA's (not shown). The actuator structure is used to move and position read/write heads at different radial positions relative to the rotational axis of a rotating disk stack (not shown), as is well known in the art.
The prior art HGA 2 also includes a flexure 18 which is fixed to the load beam 14 and which implements a gimbal 12 which permits limited relative motion of read/write head 16, which is mounted to flexure 18. A twisted pair of lead wires 28 are mechanically and electrically connected to head 16 and extend along the length of the load beam 14. The lead wires are typically encased by a dielectric tube 29 to ensure that the wires are not shorted by tabs 19, which are used to hold the wires generally fixed with respect to load beam 14. The overall mass of the wires and dielectric tube can be up to a milligram or more. More recent prior art HGA designs may employ semi tubeless wiring configurations which can result in relatively low HGA masses.
FIG. 2 shows a side view of prior art HGA 2. A portion of the HGA may optionally be prebent so that during operation, HGA 2 remains relatively straight while still applying a load force on head 16 in the direction of the disk surface (not shown), thereby reducing the z-axis (height) clearance required for the in situ HGA structure.
FIGS. 3 and 4 are respective enlarged bottom and side views of the distal portion of HGA 2 showing the prior art flexure and wire structure in greater detail. Flexure 18 is attached to the distal end of load beam 14 and implements a gimbal for interconnecting and pivotably supporting head 16 relative to the load beam. The head has a generally planar undersurface 20 which includes a pair of air bearing rails 22 which form the main air bearing surface (ABS). Each of the rails includes a taper 24 at the leading edge. The trailing edge of at least one of the rails 22 includes a read/write transducer 26. A twisted pair of fine wires 28 (two pairs for a high performance, dual element MR design) are provided to interconnect the transducer to a preamplifier circuit (not shown) or other electronic component which is typically mounted away from the HGA structure.
The invention to be described provides a robust, flexure with integral wiring and a high compliance gimbal for use with a low mass head supported on a suspension attached to an actuator in a high performance rigid disk drive.